Comparison between different models output for the peak density matching the observations and the N₂D⁺/N₂H⁺ local abundance ratio derived from the L183 observations (from Pagani et al. 2007). The error bars represent the maximum (resp. minimum) ratios using the maximum (resp. minimum) N₂D⁺ abundance profile compared to the minimum (resp. maximum) N₂H⁺ abundance profile as displayed in Fig. 4b of Pagani et al. (2007). The 7 models are listed in Table 1. The x axis is the cylindrical radius.